Without limiting the scope of the disclosure, this background is described in connection with external fixation devices and specifically connection struts and rods. Generally, external fixation devices are commonly used in a variety of surgical procedures including limb lengthening, deformity correction, fracture reduction, and treatment of non-unions, mal-unions, and bone defects. The process involves a rigid framework comprising several rings that are placed externally around the limb and attached to bone segments using wires and half pins, which are inserted into the bone segments and connected to the related section of the external rigid framework. The opposite rings of the rigid framework are interconnected by either threaded or telescopic rods directly or in conjunction with uni-planar or multi-planar hinges, which allow the surgeon to connect opposite rings that are not parallel to each other at the time of application or after manipulation of bone segments either rapidly (acutely) or gradually over a period of time.
For example, in bone fracture reduction or non-union treatment, the wires and half pins are inserted into each bone segment and attached to rings of a rigid framework. The rigid framework is used to acutely reduce a displacement and restore alignment between the bone segments. During the realignment of the bone segments, the orientations of opposite rings are often not parallel. Those opposite rings of the rigid framework are connected together by threaded or telescopic rods with attached uni-planar or multi-planar hinges. This allows the opposite bone segment to be rigidly fixed until complete fracture healing or bone consolidation is completed.
Also for example, in limb lengthening, the bone is surgically divided into two segments and wires and half pins are inserted into bone segments above and below the surgical bone cut and attached to rings of a rigid framework interconnected by struts or telescopic connection rods. The rigid framework is used to gradually push the two bone segments apart longitudinally over a period of time (e.g., one millimeter a day), which allows the bone to gradually form in the gap between bone segments created by this distraction technique. Once the desired amount of lengthening is achieved (e.g., 5-6 cm), the external apparatus is stabilized into a fixed position and left on the bone segments until mineralization of the newly formed bone is complete (e.g., 3-6 months, depending on the nature of pathology and amount of lengthening).
Similarly, in deformity correction, the bone is surgically divided (usually at the apex of the deformity) into two segments, and wires and half pins are inserted into bone segments above and below the surgical bone cut and attached to rings of a rigid framework. Opposite rings of the rigid framework are connected together by threaded rods with attached uni-planar or multi-planar hinges and an angular distractor is used to gradually push the two bone segments apart angularly over a period of time.
For various bone treatments, introducing controlled destabilization can accelerate bone healing and significantly improve the strength of the fracture callus. Gradually increasing a load is an important part of the bone healing process. To achieve such controlled destabilization, the external fixation devices can be dynamized. There are many ways of achieving dynamization, examples including, for a unilateral fixator, removing one or more of its bars, sliding the bars further away from the bone, removing pins, and/or releasing tension or compression from the system, and for a circular frame, removing one or more of its wires, releasing tension from the wires, removing connection rods between rings, removing rings from a ring block, and/or releasing tension or compression from the system. These techniques can be problematic since they often result in wide variations in the level of instability and may not effectively limit the dynamization to a desired direction or degree of displacement axis of movement.